1. Field of the Invention
The invention relates to the field of composite structure fabrication apparatus and process of making composite structures using vacuum assisted resin transfer molding techniques and, in particular, to an apparatus and process wherein duel resin distribution system improves resin infusion in the lay-up.
2. Description of Related Art
The vacuum assisted resin transfer molding (VARTM) process to make composite parts is old in the art. In general terms a dry un-impregnated fiber or fabric material is laid up in layers on top of a mold. A vacuum bag is placed about the lay-up and sealed to the mold. A peel ply may be placed on top of the lay-up and between the layers and mold surface to insure that the vacuum bag can be removed from the completed part and that the part can be removed from the mold. Resin is introduced into the vacuum bag, while a vacuum is drawn from beneath the lay-up. This causes the resin to flow through the lay-up. Thereafter, the resin flow is terminated and the resin in the assembly is cured, typically by heating to its curing temperature. To insure even distribution of resin into the lay-up, a resin distribution medium is placed on top of the lay-up, which is designed to cause the resin to evenly distribute there across eliminating resin starved areas.
Many types of resin distribution have been proposed. For example, U.S. Pat. No. 4,132,755 Process for Manufacturing Resin-Impregnated, Reinforced Articles Without The Presence Of Resin Fumes by J. Johnson. Johnson discloses the use of a perforated film between the lay-up and vacuum bag. Resin is fed from the top through the vacuum bag, through the perforated film and into the lay-up. A spring is located at the periphery of the lay-up, but under the perforated film. The spring is coupled to a vacuum line, thus providing a channel such that resin can be more readily transferred into the lay-up. This reference is of interest for disclosing the use of a perforated film and the use of a spring to provide a channel to the perforated film. However, a special perforated film is required and there is still the problem of insuring that the resin reaches all parts of the perforated film. Japanese Patent No. 60-83826 discloses the use of a wire mesh as a distribution median in a vacuum assisted molding process. However, a wire mesh may not necessarily be made to conform to a complex contoured part.
U.S. Pat. No. 2,913,036 Process and Apparatus For Molding Large Plastic Structures by G. H. Smith discloses the use of channels placed on the lay-up that act as resin distribution paths and become reinforcements on the finished part. It is unusable on parts that do not require a reinforcement.
U.S. Pat. No. 4,902,215 Plastic Transfer Molding Techniques For The Production Of Fiber Reinforced Plastic Structures by W. H. Seamann discloses, in general terms, the design of a distribution medium which includes two parts: spaced apart lines and an array of raised pillars. In detail, the distribution medium can be a crisscrossed pattern of mono-filaments with raised segments at the intersection of the mono-filaments; a series of spaced apart strips forming a grid structure; or a knitted cloth with raised segments being areas of increased bulk. A central conduit in the form of a spring is positioned over the peel ply and is in communication with the resin inlet port acts as a central distribution line. Also of interest is U.S. Pat. No 5,052,906 Plastic Transfer Molding Apparatus For The Production Of Fiber Reinforced Plastic Structures by W. H. Seemann, which discloses the use of the distribution medians disclosed in the ""215 patent on either side of the lay-up. These distribution mediums are specialized products and may unduly raise fabrication costs.
U.S. Pat. No. 5,403,537 Method For Forming composite Structures by E. C. Seal, et al. discloses a method wherein multiple layers of fibrous reinforcements are assembled into a desired configuration on a support tool, with one of layers of fibrous reinforcement defining a resin carrier fabric (distribution medium) that extends beyond the periphery of the other layers. The layers of fibrous reinforcements and tool are covered with a flexible layer to form an envelope that encapsulates the fibrous reinforcements. A vacuum source evacuating air from the envelope. Resin is introduced into the envelope and fibrous reinforcements by using a flow path through the one layer used as the resin carrier layer. After the fibrous reinforcements have been impregnated, the resin flow is terminated and the resin is cured. What is really happening is that an additional fibrous layer is added to the fiber reinforcements making up the part that extends there beyond and over flow channels at the periphery of the tool. In one embodiment, this extra fibrous layer is separated from the xe2x80x9cpartxe2x80x9d by a release or peel ply. In a second embodiment, the fibrous layer is integral with the part. This distribution medium is designed for use in a process where the resin is introduced from the peripheral edges of the lay-up.
U.S. Pat. No. 6,048,488 One Step Resin Transfer Of Multifunctional Composites Consisting Of Multiple Resins by B. K. Fink, et al. discloses a system wherein a pair of preforms with different permeabilities are installed in a mold separated by a separation layer. Different resins are injected into each preform by the vacuum assisted resin transfer method. The trick to making this process work is the use of a separation layer having permeability lower than the permeability of either of the fiber preforms.
The FASTRAC System developed by the US Army Research Laboratory is also of interest. FASTRAC uses a dual bag with in a bag concept. Both bags are sealed to the mold surface with the lay-up within the inner bag. The outer bag incorporates protrusions. A vacuum is first drawn from between the inner and outer bag. This forces the protrusions into the inner bag creating a pattern of channels. A vacuum is then drawn from between the mold surface and inner bag. Resin is then flowed into the lay-up through the channels. Thus the inner bag acts as a resin distribution medium. This apparatus requires a custom vacuum bag, which may raise fabrication costs.
Thus, it is a primary object of the invention to provide an apparatus for fabricating composite parts by the VARTM process.
It is another primary object of the invention to provide an apparatus for fabricating composite parts by the VARTM process that produces parts at a lower cost.
It is another primary object of the invention to provide an apparatus for fabricating composite parts by the VARTM process using an improved resin distribution medium.
It is a further object of the invention to provide an improved resin distribution medium for the VARTM process.
It is a still further object of the invention to provide an improved resin distribution medium for the VARTM process that uses readily available materials.
The invention is an apparatus for fabricating fiber reinforced plastic structures and a method of making same. In detail the apparatus includes a fluid impervious outer sheet having a resin inlet port. A mold surface is included upon which can be supported a lay-up of one or more layers of a fibrous material, and over which can be placed the fluid impervious outer sheet and its edges marginally sealed upon the mold surface to form a chamber. A vacuum outlet port in connected to the chamber for drawing a vacuum upon the chamber. A two-part resin distribution medium is positioned between the fabric lay-up and the fluid impervious sheet. The first part of the resin distribution medium is a resin distribution sheet having a first permeability for distributing resin throughout the lay-up. The second part includes at least one resin distribution line in the form of a flat sheet coupled to the inlet port for distributing resin throughout the resin distribution medium. This at least one resin distribution line has a second permeability equal or great than the first permeability of the resin distribution sheet. Preferably, the at least one resin distribution strip is thicker than the resin distribution sheet. A peel ply porous to resin may be positioned between the resin distribution medium and the lay-up and the lay-up and mold surface.
The method of forming the fiber reinforced plastic structures includes the steps of:
1. Placing fibrous material on a mold surface creating a lay-up;
2. Placing a resin distribution medium over the lay-up comprising a resin distribution sheet and at least one flat resin distribution line over the lay-up.
3. Placing a fluid impervious outer sheet having a resin inlet port over the fibrous material and the resin distribution medium and sealing the marginal edges thereof to the mold surface forming a chamber such that resin inlet port is in contact with resin distribution line.
4. Introducing resin into the chamber through the resin inlet port.
5. Drawing a vacuum from the chamber.
6. Curing the resin.
The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings, in which the presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention.